Many conventional applications of energy to superficial human tissue employ ablative or non-ablative lasers, radio frequency, or ultrasound. Some recent examples of such applications include that disclosed in Knowlton, U.S. Pat. No. 6,381,498 (using radio-frequency (RF), microwave or ultrasound for wrinkle reduction), in Friedman, U.S. Pat. No. 6,626,854 (employing ultrasound for lipolysis), and in Klopotek, U.S. Pat. Nos. 6,113,559 and 6,325,769 (employing ultrasound for collagen reformation). While surface ablative lasers cause severe trauma to the upper layer of the skin, such as dermis and stratum corneum, and realize a long recovery time and eventual rejuvenation of the skin, the medical efficacy and results are significant. Non-ablative lasers and RF energy sources do not cause significant trauma to the upper surface of the skin, but the efficacy of such sources is low, and with the end results being less than satisfactory.
During the last decade attempts have been made to use ultrasound in lipolysis procedures for volumetric ablation of the deep fat layer. While laboratory results of such investigative attempts may show potential promise of fat destruction in volume, the objective of such ultrasound procedures is solely to reduce the thickness of the fat layer rather than any rejuvenation of the initial superficial layer.
Currently, some suggested therapy methods aim at collagen reformation as a primary target for reducing wrinkles in the skin, including the use of connective tissue regeneration as a primary target and biological response. However, specific targeting of collagen reformation may not be the only or even a critical factor in tissue rejuvenation. For example diode lasers and intense pulsed light (IPL), which can target collagen with very high specificity, are generally yielding mixed or low efficacy results. Moreover, RF energy deposition is generally volumetric with a high gradient toward the applicator probe and has difficulties with the selectivity and placement of the energy that fundamentally is dependent on the electrical impedance of the treated tissue.